1. Field of the Invention
The invention relates to a method for channel estimation for wireless communication between a motor vehicle and another communication partner which can be a mobile communication partner or a stationary one. In the channel estimation, the result of an environment sensor system is also used.
2. Prior Art
In a digital transmission system, the data to be transmitted are initially modulated digitally. This is also called symbol mapping. In a pulse shaping filter, a continuous-time baseband signal is subsequently generated. Before the signal can be transmitted via the actual transmission channel, the baseband signal is transformed into a so-called bandpass signal, for example by means of a quadrature modulator.
At the receiver end, the received signal is transformed back into a baseband signal via a corresponding quadrature demodulator, wherein this retransformation can be followed by certain error correction mechanisms.
The transmission channel is determined by the physical communication characteristics of the system. In this context, the transmitted signal can be adapted to the characteristics of the transmission channel by a suitable choice of transmission and modulation methods in order to achieve the most optimal transmission possible. At the receiver end, a so-called channel estimation is performed in order to be able to compensate for distortions occurring due to the transmission channel. For this purpose, reference signals are frequently inserted into the data stream at the transmitter from which the receiver can derive information about the channel transmission function. The channel transmission function can be estimated on the basis of this information.
In this context, the known channel estimation methods generate a model of the environment wherein only information from the communication itself has normally been used hitherto. However, this is problematic for wireless communication with the outside world when a communication partner, for example a motor vehicle, is moving at high speed and, as a result, the environmental conditions change rapidly. This also leads to rapidly changing propagation characteristics of the wireless or radio communication.
In a motor vehicle, a multiplicity of options are known as wireless communication systems with the outside world. By means of a vehicle-to-infrastructure or vehicle-to-vehicle communication (C2X), the systems can increase the safety of the vehicle, improve mobility, and can also be used for commercial applications. Communication technologies considered here are particularly cellular communication systems, such as GPRS, EDGE, UMTS, LTE, WiMax, automotive WLAN according to the IEEE 802.11p standard, or RKE (remote keyless entry). These technologies also enable Internet access or wireless driving authorization to be implemented.
U.S. Pat. No. 6,349,119 B1 shows a method for channel estimation that estimates the characteristics of the channel between a transmitter and a receiver with high accuracy using geometric models of the channel, recognizes the position of the transmitting antennas using the geometric information, which is based on the model, and estimates the path between the transmitter and the receiver. In the case of a vehicle, the geometric information is acquired by a camera.
However, a problem with such a system is that the transmitting antennas are frequently detected only with difficulty by the cameras and elaborate image processing must be carried out in order to actually determine the positions of the cameras from the recorded image data. The method is, therefore, very elaborate and computationally intensive and will frequently not lead to satisfactory results, especially at high vehicle speeds because the evaluation of the antenna position takes too long and the relative position between transmitter and receiver has changed again by the time the transmitter position is determined.